title: Effects of odd-even side chain length of alkyl-substituted diphenylbithiophenes on first monolayer thin film packing structure.
abstract: Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5'bis(4-alkylphenyl)-2,2'-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling.
authors.affiliation: Department of Chemical Engineering, Stanford University, Stauffer III, 381 North-South Mall, Stanford, California 94305-5025, USA.
authors.forename: Hylke B
authors.initials: HB
authors.lastname: Akkerman
authors.forename: Stefan C B
authors.initials: SC
authors.lastname: Mannsfeld
authors.forename: Ananth P
authors.initials: AP
authors.lastname: Kaushik
authors.forename: Eric
authors.initials: E
authors.lastname: Verploegen
authors.forename: Luc
authors.initials: L
authors.lastname: Burnier
authors.forename: Arjan P
authors.initials: AP
authors.lastname: Zoombelt
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Saathoff
authors.forename: Sanghyun
authors.initials: S
authors.lastname: Hong
authors.forename: Sule
authors.initials: S
authors.lastname: Atahan-Evrenk
authors.forename: Xueliang
authors.initials: X
authors.lastname: Liu
authors.forename: Alán
authors.initials: A
authors.lastname: Aspuru-Guzik
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: Paulette
authors.initials: P
authors.lastname: Clancy
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao